The project will analyze the lethal and kinetic effects of antitumor agents on various established human colon carcinoma cell lines as a function of drug concentration, exposure time, and position of the cells in the cycle at the time of drug administration (cell cycle stage-dependent function). Cell kill will be assessed by the reduction in colony forming capacity. Effects on cycle progression will be defined by sequential DNA histograms obtained by pulse cytophotometry. Combination chemotherapy using drug pairs will be conducted to define the mechanisms of cell killing potentiation. Paired treatment will be conducted in simultaneous or staggered fashion. Methods will be developed to study the response of resting phase populations by the use of plateau phase cultures and multicellular spheroids. These investigations on drug effects at the cellular level should contribute a rationale guideline for developing superior clinical therapeutic protocols.